Spherical double electric layer structure of C20F20 and its endohedral complexes X@C20F20 (X = O2−, S2−, Se2−)

The structures and stabilities of cage C20F20 and its endohedral complexes X@C20F20 (X = O2−, S2−, Se2−) were determined at the B3LYP/6-31G(d) levels of density functional theory (DFT). It is found that cage C20F20 (Ih) possesses of a distinct Cδ+-Fδ− spherical double electric layer, and the adiabatic electron affinity (EAad) of host cage is higher than that of isolated O atom (2.63 vs. 1.46 eV). This suggests the C20F20 cage can selectively trap and stabilize the capsulated spherical anions. The calculations predict that all guest species are minima at the cage center and the corresponding X@C20F20 (Ih) complexes have negative inclusion energies (ΔEinc) and thermodynamic parameters (ΔZ). The amount of charge that is being transferred from the encapsulated anions to the cage increases with the atomic radius, i.e., from O2− (∼54%), S2− (∼114%) to Se2−(∼130%), and such a novel model of cage may have practical uses as potential and electrical building units of nanoscale materials.